In a 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP for short below) long term evolution (Long Term Evolution, LTE for short below) or long term evolution advanced (LTE-advanced, LTE-A for short below) system, an orthogonal frequency division multiple access (Orthogonal Frequency Division Multiple Access, OFDMA for short below) manner is generally used as a downlink multiple access mode. Downlink resources of the system are divided into orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM for short below) symbols in terms of time, and are divided into subcarriers in terms of frequencies.
According to an LTE release 8, 9, or 10 (LTE Release 8/9/10) standard, one normal downlink subframe includes two timeslots (slots), where a timeslot includes 7 OFDM symbols, and a normal downlink subframe includes 14 or 12 OFDM symbols in total. In addition, the LTE Release 8/9/10 standard defines the size of a resource block (Resource Block, RB for short below). One RB includes 12 subcarriers in a frequency domain, and includes one half of a subframe duration in a time domain (one timeslot), that is, it includes 7 or 6 OFDM symbols. A subcarrier in an OFDM symbol is referred to as a resource element (Resource Element, RE for short below). Therefore, one RB includes 84 or 72 REs. In a subframe, a pair of RBs in two timeslots is referred to as a resource block pair (RB pair, RB pair for short below). In actual transmission, a resource block pair used for physical resources (physical RB pair) is also referred to as a physical resource block pair (Physical RB pair, PRB pair for short below). The PRB pair is generally briefed as a PRB. Therefore, the PRB, PRB pair, physical resource block, and physical resource block pair in the following description all refer to a PRB pair.
Data of all types borne in a subframe is organized and mapped onto various physical channels based on division of physical time-frequency resources in the subframe. Various physical channels may be generally classified into two types: control channels and traffic channels. Correspondingly, data borne in a control channel may be referred to as control data (or control information), and data borne in a traffic channel may be referred to as service data. An ultimate purpose of communication is to transmit service data. A function of the control channel is to provide assistance in transmission of service data.
A complete physical downlink control channel (Physical Downlink Control Channel, PDCCH) is formed by one or more control channel elements (Control Channel Element, CCE for short below), and one CCE is formed by 9 resource element groups (Resource Element Group, REG for short below), where one REG occupies 4 REs. According to LTE Release 8/9/10, one PDCCH may be formed by 1, 2, 4, or 8 CCEs, respectively corresponding to aggregation level 1, 2, 4, or 8.
In the LTE system, due to introduction of technologies such as multiple input multiple output (Multiple Input Multiple Output, MIMO for short below) and coordinated multiple points (Coordinated Multiple Points, CoMP for short below), the capacity of a control channel is limited. Therefore, an enhanced physical downlink control channel (Enhanced PDCCH, E-PDCCH for short below) transmitted based on a MIMO precoding mode is introduced. The E-PDCCH may be demodulated based on a UE-specific reference signal demodulation reference signal (Demodulation Reference Signal, DMRS for short below).
For the E-PDCCH, there are N enhanced control channel elements (Enhanced Control Channel Element, eCCE for short below) in one PRB pair, where N is a positive integer.
According to different transmission modes, E-PDCCHs may be classified into localized (localized) E-PDCCHs and distributed (distributed) E-PDCCHs, where a localized E-PDCCH is transmitted by using a localized transmission mode, and a distributed E-PDCCH is transmitted by using a distributed transmission mode. For the localized E-PDCCH, one control channel is generally located in one PRB pair. For the distributed E-PDCCH, one eCCE is further divided into at least one enhanced resource element group (Enhanced Resource Element Group, eREG for short below). The at least one eREG may be distributed in multiple PRB pairs, so that a frequency diversity gain is obtained.
For the distributed E-PDCCH, interleaving is performed in units of eREGs in the prior art to obtain the position of one distributed E-PDCCH in a PRB pair. It is assumed that a PRB pair includes 4 eCCEs, and that an eCCE includes 4 eREGs. It is assumed that the E-PDCCH of UE1 uses the distributed transmission mode, and is located in 4 PRB pairs with index numbers 3, 4, 8, and 9. If mapping is performed in units of eREGs, 16 eREGs to which an E-PDCCH at aggregation level 4 is mapped may be located in 16 different eCCEs, and 8 eREGs to which an E-PDCCH at aggregation level 2 is mapped may be located in 8 different eCCEs.
A base station (evolved NodeB, eNB for short below) needs to transmit E-PDCCHs to multiple UEs, where some UEs use distributed E-PDCCHs, and some UEs use localized E-PDCCHs. Using an E-PDCCH at aggregation level 4 as an example, according to the mapping mode, in the 4 PRB pairs with index numbers 3, 4, 8, and 9, a part of eREGs on each eCCE are occupied by the E-PDCCH of UE1. If the eNB transmits the E-PDCCH to UE1 according to the mapping mode, the eNB cannot transmit a localized E-PDCCH in the 4 PRB pairs. Therefore, the E-PDCCH multiplexing efficiency is relatively low.